How to make an external interrupt occur with ID bit of PSW set to 0?

Question:

I want an external interrupt to occur but the interrupt request is not acknowledged.
The ID bit of the PSW is set to 0, the interrupt request is reset, and interrupt processing is enabled.

Answer:

Possible causes are as follows:
- A mask is set for the interrupt (bit 6 of the interrupt control register is set).
- NMI processing is in progress (the NP bit of the PSW is set).
- Processing of a higher priority interrupt is in progress (check using the ISPR register).
- Consecutive instructions that do not acknowledge an interrupt exist.